This invention relates to novel polyimides derived from alicyclic dianhydrides. This invention further relates to a process for synthesizing said polyimides.
Polyimides are generally considered to be high performance materials because of their excellent mechanical properties and thermal and oxidative stability. Polyimides are extensively used in place of metals and glass in many applications throughout industry, particularly in automotive, aerospace, electronic, and packaging applications. Polyimides possess utility in a wide variety of applications as films, fibers, molded articles, foams, adhesives, coatings, and the like.
Polyimides are generally synthesized in a two step process in which a dianhydride is reacted in a dipolar aprotic solvent with a diamine to form the corresponding polyamic acid, which is then thermally or chemically cyclized to the polyimide. Commonly used dipolar aprotic solvents include dimethylformamide, dimethylacetamide, dimethylsulfoxide, and N-methyl-2-pyrrolidinone. The first step of the reaction to form the polyamic acid is generally carried out at temperatures below about 60.degree. C., in order to prevent premature cyclization and thereby maintain solubility, since known aromatic polyimides are often insoluble in common organic solvents. In such cases, the desired article is formed from the soluble polyamic acid and the article is then thermally or chemically imidized. Thermal imidization is usually carried out between about 150.degree. and 300.degree. C. Alternatively, cyclization can be effected by use of a chemical dehydrating agent such as acetic anhydride in pyridine.
The problem associated with many of the known aromatic polyimides is that such polyimides are often insoluble in common organic solvents and thus require a two step fabrication process in which the polyamic acid is formed into the final article which is then converted to the polyimide. What is needed are polyimides which are soluble in common organic solvents and therefore are directly processable into articles in a single fabrication step. Such polyimides should also possess good thermal and mechanical properties.